It is generally accepted that the aging infrastructure worldwide is fast approaching originally designated design lives. Specifically, pipes and conduits located both above and below ground employed in the conveyance of liquids frequently require repair to prevent leakage into the system as well as preventing fluid from the leaving the system. The cause of leakage can vary from improper installation to environmental conditions to normal aging or the detrimental effects of the substances transported on the pipe materials. Regardless of the cause, leakage is undesirable. The United States Congress and the US Environmental Protection Agency have both mandated reductions in such leakage through such means as the Clean Water Act.
Because of the high costs and the level of difficulty involved in excavating or removing and replacing leaking conduits, various methods have been devised for insitu repair. These methods have minimized the expense and hazards associated with digging and replacing defective pipes.
In the conventional processes for the insitu rehabilitation of existing pipes and conduits, a flexible tubular liner impregnated with a thermosetting synthetic resin matrix is introduced into the conduit using an inverting process as well know to one skilled in the art. In U.S. Pat. No. 5,108,533, the flexible tubular liner is comprised of a needle-punched felt material. In conditions where the intersecting angles of the main pipe and the lateral pipe constitute an obtuse angle, as typically encountered in a convention sewer “wye”, a needle-punched felt material does not possess the necessary flexibility to conform well to the surrounding pipe walls.
Once the liner is positioned within the pipeline, the liner is pressurized internally using a fluid pressure such as air or water to force the lining material into intimate contact with the pipe interior and provide compaction. Adding heat in the form of hot water, steam or electrical energy can then cure the resin matrix. The latter method of providing heat by electrical energy is disclosed in U.S. Pat. No. 5,606,997. Once the resin is cured, the resultant material forms a hard, tight fitting lining within the pipe that also serves to provide added structural support.
In the repair of sanitary sewer systems for instance, a main trunk line is used for the transportation of effluent from various intersecting piping systems to an end location. The majority of work to date has focused on the repair and rehabilitation of the main trunk lines. Even after much effort and expense has been expended on the remediation of these systems, the areas of confluence between the main lines and intersecting side lines (hereinafter called laterals) has only minimally been addressed. In a typical municipal sewer system, a plurality of laterals can exist in every mainline section. With as many as 10 laterals on a typical residential street, the potential for fluid ingress and egress at the lateral to main interface is great.
Only several processes are known that address repair of the lateral to main interface. One such process is described in U.S. Pat. No. 5,223,189 wherein a thermoplastic sealing bushing including an internal heating element is installed into the lateral opening from within the mainline by means of a robotic device and an expandable mandrel. This method relies on a heat formed seal being produced between the bushing and a pipeline lined with a similar, compatible thermoplastic material. In U.S. Pat. No. 5,950,682, a resin absorbent material, impregnated with a hardening resin matrix, is positioned within the mainline pipe and provides a means for inverting a section of like material into the lateral pipe for a pre-determined distance. Because these systems and, systems similar to this use a resin matrix that is expected to fully cross-link or cure in an undesirable environment (i.e. hot, cold, wet, etc), catalysts, initiators and even inhibitors are added to the resin system in an attempt to control the curing mechanism. This has resulted in many failures due to premature curing of the resin, inadequate resin cross-linking and shrinkage. In addition, because the resin is applied to the repair material at the installation site, inconsistencies in both resin content and mixing procedures can be expected. Other methods have been disclosed that use an auxiliary curing source unlike the typical systems that rely solely on ambient temperatures to effect a cure. Radiant energy in the form of ultraviolet light, as in U.S. Pat. No. 5,915,419, or visible light, as disclosed in U.S. Pat. No. 4,518,247 have been employed to provide a curing mechanism for lateral interface sealing systems. The shortcomings of these types of systems lay in the difficulty of the prescribed radiant light source to penetrate through the thickness of the repair material and the overall fragility of such devices.
Therefor, it is desirable to provide a system to overcome the constraints mentioned above and also afford a fast, consistent repair method that enables robust, cost effective reconstruction of the lateral to mainline interface.
Another problem is encountered with repairing pipes having large diameters. Various methods exist for rehabilitating damaged sanitary sewer conduits with diameters exceeding about eighteen inches. These methods include physical removal of the damaged section of the conduit, and replacement of the damaged section. A more common method is the use of a reinforced liner having dimensions similar to the dimensions of the damaged portion of the conduit.
Liners are typically formed from composite materials and can be impregnated on-site, or pre-impregnated with a curable resin. When the resin is cured, it hardens and the liner forms a protective shell in the section of the conduit where it is placed. There are two primary methods to cure the resin, ambient cure and heat activated cure, including hot water or steam cure.
Ambient curing suffers from a number of disadvantages. If the ambient temperature is too low, which is common with underground conduits, the resin will not completely cure and the liner can collapse. In contrast, if the ambient temperature is too high, the resin can cure prematurely, that is before the liner is properly located in the damaged portion of the conduit.
There are a number of disadvantages to curing a liner with hot water or steam. First, the equipment required to heat the water or to create steam is extremely expensive and inefficient. Second, curing with either fluid requires a temperature ramp-up, which consumes long periods of time. For example, the water temperature must be held at approximately 135° F. for several hours, and then increased to 180° F. for several more hours. For a ninety-six (96) inch conduit, the curing process can last between three to seven days.
Curing a liner with hot water, steam, or ambient is also negatively affected by heat sink in the conduit. The heat sink is greater on the lower portion of the conduit than on the upper portion of the conduit. This result occurs because the lower portion is typically wet, while the upper portion remains dry. This is especially true in a gravity conduit that is not fully charged. The wet lower portion of the conduit draws a greater amount of heat, q, from the heat source than does the dry upper portion. The heat flux, q″, in the lower portion of the conduit is greater than the heat flux in the upper portion of the conduit. As a result, a greater quantity of heat is required to cure liner in the lower segments of the conduit than liner in the upper segments of the conduit. In addition, heat sink can prevent the complete curing of all resin in the liner, thereby reducing the strength and durability of the liner. These factors reduce both the cost efficiency and process efficiency of hot water, steam, and ambient cure.
The conventional liners used to repair large diameter conduits are very thick and generally require a large amount of resin. The large amount of resin exacerbates the need for ramped temperatures and as a result, further increases curing times while reducing the efficiency of the repair. Due to their large size and weight, liners for large diameter conduits are difficult to handle and maneuver within the damaged conduit. Also, liners for large diameter conduits are more susceptible to the negative effects of heat sink.
One aspect of the present invention is provided to solve these and other problems.